SO Answer

http://stackoverflow.com/questions/36181072/how-can-i-display-html-elements-based-on-os/36182132#36182132

by enigmarm

HTML

<button onclick="loadBrandsPage()">Go!</button>
<p id="brandsmac" class="brand">
You have a Mac!
</p>

<p id="brandspc" class="brand">
You have a Windows!
</p>

CSS

.brand {
  display: none;
}

JavaScript

(function loadBrandsPage() {
    var OSName="Unknown OS";
    if (navigator.appVersion.indexOf("Win")!=-1) { 
        OSName="Windows";
    } else {
        OSName="MacOS";
    }
    if(OSName == 'Windows') {
        document.getElementById("brandsmac").style.display = 'none';
        document.getElementById("brandspc").style.display="block"; 
    }
    if(OSName == 'MacOS') {
        document.getElementById("brandsmac").style.display="block";
        document.getElementById("brandspc").style.display = 'none';
    }
})();